Gamma Radiation Methods in Characterizing Horizontal and Vertical Multiphase Flow

Abstract

Pressure drop and stability characteristics of the flow in subsea flowlines are important to the proper operation of offshore platforms, and they depend intimately on the flow regimes that occur. Air-oil-water three phase flows in simultaneous horizontal and vertical pipe orientation are presented. Fast-sampling (250 Hz) gamma densitometer units were installed at the top of the 50.8mm diameter, 11m high vertical riser and horizontally near the riser base in the Cranfield University multiphase flow test facility. Gamma radiation attenuation data were collected from the caesium-137 radioisotope-based densitometer for a range of air-oil-water flow mixtures spanning the facility's delivery range. Examination of the gamma densitometer signal response revealed the presence of quasi-periodic waveforms in the time-varying multiphase flow densities. The probability mass function (PMF) characteristics predict the flow in the horizontal flow loop as bubbly, slug and wave flows while the vertical riser flow regimes were bubble, slug and churn. Flow pattern maps were then developed based on these PMF plots for both horizontal and vertical pipe orientation. The effect of upstream conditions on the vertical riser flow behaviour was also investigated via two different air inlet configurations: (i) upstream flowline mixing and (ii) riser base injection. No significant difference exist in flow behaviour at low superficial air-liquid velocities for both configurations, but at higher superficial airliquid velocities, the intermittent flow behaviour due to hydrodynamic slugging in flowline influences the riser flow pattern characteristics, thus controlling the riser dynamics.